The manner in which different pharmacologic agents utilize or depend upon cellular Ca ions sites or stores for theinitiation of contractile responses in rabbit aortic smooth muscle will be examined. The effects of norepinephrine, histamine, serotonin, angiotensin and potassium on contractile responses, ionic concentrations and Ca45 distribution and movements in isolated aortic smooth muscle in the presence and absence of Ca ions-depletion, lanthanum and other selected rare earth ions and procaine will be delineated. Conventional techniques will be employed for measurement of isometric tension responses, for Ca45 uptake and rapid washout, and for total Ca ions, Na and K ions concentrations. Experiments will be designed to elucidate the manner in which the actions of different stimulatory agents depend upon cellular Ca ions sites or stores as well as the nature of Ca45 uptake and retention. This information could provide a basis for evaluation of ideas concerning the mechanisms by which membrane-bound Ca ions is involved in events leading to alterations in contractile tone. In addition, Ca ions antatonistic actions of the aminoglycoside antibiotics (neomycin, streptomycin, kanamycin and gentamicin) will be examined with similar techniques in rabbit aortic smooth muscle and in such peripheral vascular systems as dog mesenteric and femoral arteries. Thus, information will be obtained concerning the cellular actions of these antibiotics in several vascular smooth muscle preparations.